This invention relates broadly to rocket motor construction. More specifically, it relates to means for mounting solid propellant grains in rocket motor cases so that stresses induced by propellant shrinkage or differential thermal expansion or contraction thereof relative to the case are obviated.
A continuing problem with solid propellant rocket motors, particularly those of the end-burning type, is that most solid propellants tend to shrink during the curing process, and also tend to contract to a much greater extent than the rocket motor case to which they are bonded during the subsequent cooling period. The primary problem in such mounting means is to provide for axial motion of the propellant grain relative to the case and at the same time prevent ignition of the sides of the propellant during rocket motor operation. Conventional means of obviating these stresses have included the use of a plurality of layers of insulation surrounding the propellant grain. These layers are bonded together and to the case of the rocket only at the forward end thereof to permit longitudinal movement of the propellant grain relative to the case as it shrinks or expands. This method tends to add an unacceptable amount of inert weight to the rocket and to diminish the quantity of propellant that can be loaded therein. My previous invention cited above as a related application, and over which the present invention is considered an improvement, treated this problem by bonding a series of overlapping hoops to the propellant grain and to the case in such a way that a series of longitudinal expansion joints were created. Although this is a useful invention, the present invention is much lighter in weight of inert parts.